The British Olympic Association board has upped the ante in its contractual row with the 2012 organisers, Locog, claiming it would never have signed a contract to host the Games if there was no guarantee of a "significant" share of the operating profit.

As the sports minister, Hugh Robertson, said he would not intervene in the dispute following a meeting with the BOA chairman, Lord Moynihan, representatives from the Olympic sports gathered in London to be updated on the situation.

David Hemery, the BOA vice‑chairman who was on the board when the original host‑city contract was signed, wrote an open letter to the sports in which he insisted the BOA was led to believe the "real prize" from the Games would be a "significant financial legacy".

The BOA, which is taking the row to the court of arbitration for sport despite the International Olympic Committee taking Locog's side, insists any post‑Games surplus should be calculated without taking any costs that could be attributed to the Paralympics into account. On that basis, it says the surplus could be as much as £400m.

Any surplus would be divided 20-20-60 between the BOA, the IOC and grassroots sport. But Locog claims it has always aimed to break even and has treated the Olympics and Paralympics as an integrated whole.

"Our board would never have so enthusiastically voted in favour of the proposal if we anticipated that in fact there would be no balanced budget, with no sporting legacy beyond buildings in London," wrote Hemery. "To assert we knew this all along is an insult to the common sense decision making of the board members of that time."

Moynihan said he was "increasingly confident" that £5m due to the BOA under a separate element of the joint marketing agreement with Locog would be delivered but reiterated he would fight on over what he called the "legacy element". He again insisted that Locog's finance director had first mentioned the £400m figure at a meeting with the BOA, despite Neil Wood explicitly denying it earlier this week.

Robertson said he would not act as a mediator. "The Government is not and cannot be a mediator in a dispute between two private companies and I reiterated that there was no additional government money available to help solve the dispute," he said. "I have encouraged the BOA to resolve the matter as quickly as possible in order to allow everyone to get back to making preparations to ensure 2012 is a great success."

The row has come as an embarrassment to Games organisers in the week that the IOC inspection committee has arrived to check on preparations.